1. Technical Field
The present invention relates to optical instruments and more particularly, to optical instruments exhibiting at least two optical paths.
2. Discussion of the Related Art
Optical instruments that comprise an objective lens with a bore cut substantially through its center are known in the art. The bore is usually used to accommodate optical and other elements that may be used to establish an alternative optical path other than the optical path associated with the objective lens.
FIG. 1 shows an optical instrument enabling two optical paths that share a common optical axis, according to an exemplary embodiment of the existing art. Optical instrument 10 comprises an objective lens 11 and a set of objective lenses 12 located within a bore cut through substantially the center of objective lens 11 such that the elements of set of objective lenses 12 are located substantially along the optical axis of objective lens 11. Rays coming through objective lens 11 pass through diverging lens 14 and converging lens 15 both located along the optical axis of objective lens 11 and configured, in combination, to produce a first image at plane 16.
Optical instrument 10 further comprises a first reflective element 13 located along the optical axis of objective lens 11 and tilted at an angle being approximately 45° such that rays coming through set of objective lenses 12 are folded onto an optical axis that is substantially perpendicular to the optical axis of objective lens 11. First reflective element 13 may be physically attached, via support elements (not shown) to a housing (not shown) that accommodates the optical elements of optical instrument 10. The support elements are required since set of objective lenses 12 usually extend further into optical instrument 10 beyond objective lens 11.
A second reflective element 17 is positioned along the optical axis of the folded rays and tilted at an angle being approximately 45° such that the folded rays are folded again onto an optical axis that is substantially parallel to the optical axis of objective lens 11. A set of lens 18 is located along the optical axis of the rays folded by second reflective element 17. The lenses of set of lens 18 are configured to create a second image at plane 19.